1. Field of the Invention
The present invention relates to heat exchangers and, in particular, to radiators employed with internal combustion engines used in motor vehicles.
2. Description of Related Art
It has become common practice to use plastic tanks, usually made of glass-reinforced nylon 6/6 material, on heat exchangers with headered cores of brazed aluminum construction. Such heat exchangers include engine-cooling radiators, heaters and some intercoolers, primarily for automobile use. This plastic tank/aluminum (PTA) heat exchanger construction technique is also being used in some heavy-duty truck radiator applications. The problem with typical PTA construction is that it has always been considered inferior to more robust construction methods, such as tanks with gasketed, bolted tank-to-header joints, or soldered or welded tank-to-header joints. Such a judgment stems from the fact that the foot of a plastic tank is typically secured to a shallow groove in the aluminum header by means of bending tabs, which are part of the header, over the tank foot, with a rubber gasket seal between the tank foot and the bottom of the groove. When pressure is applied to the inside of the tank during operation, the tank foot tends to move upwards in a direction that tends to unbend the tabs. With repeated cycles of pressure, the tabs weaken, the compression on the gasket is relieved, and leakage of coolant to the outside occurs.
Other weaknesses of typical PTA construction include flexing of the plastic tank under cyclic pressure and temperature conditions, contributing to movement of the tank foot within the header groove, resulting in leakage. In addition, the header tab material is rendered soft by the core brazing process, making it prone to unbending during operation, leading to reduced pressure on the gasket and, ultimately, leaking. The gasket material chosen for PTA construction is not always of high quality sufficient to resist aging and stiffening under high temperatures. This is often the cause of leaking in PTA radiators. Such leaking problems are the reason for the poor reputation of PTA heat exchanger construction compared to more traditional construction methods. However, PTA construction readily lends itself to high volume, low cost production. If means could be found to overcome the shortcomings of PTA construction, it would be a welcome improvement.